A lot of people just don't care for the way the notes on the B string sound. I just made my recent foray from the 4-string-only world to a 6-string, and to be honest...I'm not crazy about the B string, at least not on my bass.

He needs to go back and teach himself a few things then (maybe how to play with a low B). In today's world, a bass teacher needs to be able to do that. I mean, you pay him for lessons, right? I might be inclined to find a teacher who accepts students regardless of whether they have a low B, high C, or both!